1. Field of the Invention
The present invention relates to a method and apparatus for mitigation of photoresist line pattern collapse in a photolithography process by applying a gap-fill material treatment after the post-development line pattern rinse step, and subsequent removal thereof to expose the line pattern.
2. Description of Related Art
Photolithography processes for manufacturing semiconductor devices, liquid crystal displays (LCDs), and photovoltaics generally coat a layer of radiation-sensitive material, such as photoresist, on a substrate, expose the radiation-sensitive material coating to light to impart a latent image line pattern, and develop the exposed radiation-sensitive material coating to transform the latent image line pattern into a final image line pattern having masked and unmasked areas. Such a series of processing stages is typically carried out in a coating/developing system.
Feature sizes of semiconductor device circuits have been scaled to less than 0.1 micron. Typically, the pattern wiring that interconnects individual device circuits is formed with sub-micron line widths. In the post-development phase of a photolithography process, once a photoresist line pattern has been already formed, a deionized water rinse step is used to remove the developer from and clean the developed line pattern. Following the rinse step, the photoresist line pattern and substrate are dried so the substrate can be transported to the next processing tool for the next processing step. During the drying step, capillary forces arise at the interfaces between the deionized water or other rinse liquid, ambient air, and the photoresist material. The tighter the photoresist line pattern (i.e. the smaller the line pattern pitch), the larger the capillary forces become, and in some cases these forces can overcome the mechanical strength of the photoresist line pattern itself, leading to line pattern collapse. Once collapsed, the photoresist line pattern does not anymore represent an exact image of the image line pattern applied to the photoresist during the exposure step, leading to lower device yields, etc.
A number of ways have been used to mitigate line pattern collapse generally involving reducing the surface tension of the rinse liquid in contact with the photoresist. For example, a surfactant can be added to the rinse liquid (e.g. deionized water) to reduce the surface tension, and hence capillary forces acting upon the photoresist line pattern during the drying step. Another approach involves adding a reactive additive to the rinse liquid (e.g. deionized water), to react with the polymeric photoresist material, with the effect of modifying the surface energy of the photoresist and hence lowering the contact angle (i.e. wetting angle) and capillary forces. However, these methods may have limitations. For example, surfactants compatible with the photolithography process and materials can only reduce the surface tension a certain amount, and a larger reduction may be necessary to overcome the increase of capillary forces due to photoresist line pattern pitch reduction in newer generations of semiconductor devices. Therefore, there exists a need for a method of mitigating photoresist line pattern collapse without the above shortcomings, and which will be effective for next generations of semiconductor.